The present invention relates to holographic imaging and particularly to unambiguous reconstruction of holographic images.
In conventional holographic imaging a hologram is generated from spatial interference between radiation reflected from an object to be imaged and radiation from a reference source. FIG. 1 illustrates one possible geometry for recording a holographic image wherein a laser 10 emits radiation 11 toward an object field containing a reference reflector 12 and an object 14. The intensity of the radiation in the object field is represented by Gaussian intensity curve 16. In the illustrated example the reference reflector 12 is a retroreflector which provides a strong reflected signal 13 toward laser 10 and thereby acts as a reference source for generation of a hologram. Object 14 is assumed to be a diffuse reflector which scatters the illuminating radiation from laser 10 in many directions as illustrated by scattered radiation 15.
The interference pattern of the radiation reflected by reference reflector 12 and object 14 is detected in holographic plane 18 and appears as a holographic interference pattern as shown generally in FIG. 2. The holographic interference pattern or hologram may be used to construct a holographic image of object 14, either optically or by numerical computation, such as computer algorithm.
In conventional holography the reference source 12 must be displaced from the object 14 to be imaged because the reconstructed image 20, shown in FIG. 3 will include two images 21, 23 of the object 14 on opposite sides of the reference source location. This results from the fact that the interference pattern or hologram does not contain information concerning the direction (positive or negative) of the offset of the object 14 from reference source 12. The reference must accordingly be displaced from the object so that the two images 21, 23 do not overlap, causing image confusion.
It is an object of the present invention to provide a method of holographic imaging which provides an unambiguous holographic image.
It is a further object of the invention to provide a method for unambiguous holographic imaging of an object utilizing a reference source within the object.
It is a further object of the invention to provide a method for holographic imaging of an object using a reflection from the object as a reference.